How do I know to register for Congestion Charge?

I live in Cheshire and drove into central London this week for the first time ever. I had heard about the congestion charge and that you get your number plate photographed and sent an invoice...yet it's for £50 if I pay immediately or else £150!!

Being someone from outside London / South East, how am I supposed to know that you have to register first to pay the standard £8 charge?

Just to clarify...I did get picked up by the camera and received a bill for £50 fine.

My point was, people living in London / South-East presumably have been made aware by the Mayor / media precisely how the charging and payment system works?

For someone outside the area, where the media has simply reported 'there is a congestion charge, photo technology is being used and you will receive a bill if you have not registered", how are they supposed to know the bill you receive is actually a fine for not knowing how to pay.

Thanks for the helpful comment Ivanhow, but I was aware I was in the C-zone and assumed I would be sent a bill for the charge (£8) not a fine. Please tell me where on the C-zone signs it says if you have not registered / paid you will be fined?

There are clearly marked road signs that warn you BEFORE you go into the zone that you are about to go in the zone and (I'm pretty sure about this) giving you a number to call.

When I google "congestion charge paying", the first answer is a summary of how and where to pay, and the third answer is the website for CCLondon (the body in charge). They're hardly keeping it a secret.

If you were unable to use a computer on the day in question to check what you needed to do, then the simple method of asking anyone on the streets (perhaps another car driver) would have easily got you the info you would have needed.

Failing that any of the shops, petrol stations, etc displaying the pretty clear "C" sign on posters saying things like "You can pay your C-Charge here" might have given you a clue.

And the idea that they would send you a bill, rather than you actually having to take the initiative and pay yourself, is delightfully quaint but I struggle to think of any other life situation where it works like that.